Manganese carbonate is a widely used colorant used in ceramic glazes and clay bodies, mainly for various earthy tones, including brown, black and purple. It is also used to produce spots in fired clay bodies and helps to increase the opacity and matte effect of low-temperature glazes. The carbonate form is generally preferred to the oxide form because it disperses better in glazes, resulting in more uniform color.
Here is a more detailed classification:
Coloring:
Manganese carbonate decomposes into manganese dioxide (MnO2) and carbon dioxide (CO2) when heated.
In alkaline glazes it can produce bluish purple and plum colors, while in leaded glazes it can produce purple-brown.
It can be used to make metallic, black, brown or purple/plum glazes.
It can be used to color pottery and give a speckled effect.
Other Uses:
Flux:
Manganese carbonate acts as a flux in glazes, reducing firing temperatures.
Clay bodies:
Manganese carbonate can be added to clay bodies to produce a speckled effect when fired.
Brickmaking:
In the brickmaking industry, manganese carbonate is used to change the base color or produce speckled bricks.
Dispersibility:
The carbonate form is known to disperse better in glazes than the oxide form, giving a more uniform color.
Crystallization:
In glazes, manganese will crystallize and precipitate out of the melt when used in large quantities, which may be the desired effect.
Important Notes:
Decomposability:
Manganese carbonate will decompose at high temperatures, so this must be considered when formulating glazes.
Concentration:
The amount of manganese carbonate used will affect the color and other characteristics of the glaze or clay body.
Glaze Type:
The type of glaze (basic, lead, etc.) will affect the color produced by manganese carbonate.
